Left Atrial Appendage

The left atrial appendage can be seen on some transthoracic
adult studies.

The left upper pulmonary vein is adjacent to the left atrial
appendage. They are separated by a fold of tissue which can be
quite visible on both transthoracic and transesophageal
echocardiography. A
persistent left superior vena cava
occupies this space when it is present.

The tissue fold may resemble a mass on some transthoracic images
as shown above, and indeed, quite often does so on transesophageal
images, as shown below.

Ligament of Marshall

This vestigial fold of the pericardium contains fibrous
bands, small blood vessels and nervous filaments surrounded
by fat.
It courses obliquely above the left atrial appendage and
lateral to the left superior pulmonary vein.
It contains the oblique vein of Marshall that drains
into the coronary sinus.

Original description by John Marshall:
On the development of the great anterior veins in man and
mammalia: including an account of certain
remnants of foetal structure found in the adult, a comparative
view of these great veins in the different mammalia, and an
analysis of their occasional peculiarities in the human subject.
Phil Trans R Soc Lond 1850;140:133-69

Unusually serpiginous left atrial appendage.

Normal Doppler flow pattern in the left atrial appendage.
There is appendage emptying following the P wave and
appendage filling following the QRS.